Reprint 633

Recent Developments on Meteorological Information Datalink

at the Hong Kong International Airport

M.K. Song

International Symposium on Electronics in Air Transport Industry

(SEATI) 2006, Hong Kong, China, 8 - 9 March 2006

RECENT DEVELOPMENTS ON METEOROLOGICAL

INFORMATION DATALINK AT THE HONG KONG INTERNATIONAL AIRPORT

M.K. Song

Hong Kong Observatory

134A Nathan Road, Kowloon, Hong Kong, China

ABSTRACT

Prompt transmission of the latest weather information and alerts to aircraft is

essential to their safe landing and taking off at the airport. With recent advances in

telecommunications technology, it has become viable for the digital transmission of weather

information directly to the cockpit as well as meteorological data collected on-board aircraft

to the meteorological office. This paper describes recent developments in meteorological

data downlink and uplink to enhance the weather service, including the application of

automatic AMDAR observations for low level windshear reporting as well as the potential

use of standard ARINC 623 message type ‘Terminal Weather Information for Pilots (TWIP)’

in existing available ACARS facilities to uplink text based windshear/turbulence alerts to

aircraft to enhance aviation safety.

1 Introduction

At SEATI 2003, the Hong Kong Observatory (HKO) presented a paper titled “Recent

Developments to Enhance Windshear and Turbulence Alerting at the Hong Kong

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International Airport” (Shun et al, 2003), which highlighted the benefits of uplink and

downlink of meteorological information in the context of windshear and turbulence alerting.

The major benefits are the improvement of the timeliness and accuracy of weather forecasts

from the availability of weather data collected onboard the aircraft downlink to the

meteorological offices and enhancement of pilots’ awareness on weather situation through

uplinking of weather products to the cockpit. The emerging communications technologies

and potential application of new uplink/downlink of meteorological information to/from

aircraft offer great potential in improving the aviation weather services, thereby enhancing

aviation safety, regularity and efficiency. The following paragraphs will present recent

developments and applications of meteorological datalink at the Hong Kong International

Airport (HKIA).

2 Downlink of Meteorological Data 2.1 Background

A number of facilities for downlink of meteorological information from aircraft have

become available in recent years. These include:

(a) Automatic Dependent Surveillance (ADS) datalink

ADS is an air traffic management datalink application specified in the Standards of

the International Civil Aviation Organization (ICAO). It is primarily used for

aircraft surveillance and air-ground communication, and they are also capable of

transmitting aircraft weather reports including wind, temperature and other optional

elements such as humidity and turbulence. HKO conducted trials with the Hong

Kong Civil Aviation Department (CAD) during 2000-2001 to demonstrate the

capability of automatic reception of aircraft weather data via ADS.

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(b) Aircraft Meteorological Data Relay (AMDAR)

AMDAR – stands for “Aircraft Meteorological DAta Relay”, through which aircraft

weather observations (wind, temperature, and other optional weather elements

measured along the aircraft flight path) are transmitted automatically to the

meteorological offices. AMDAR is a World Meteorological Organization (WMO)

programme, which aims to enhance aviation safety and efficiency through promoting

upper-air weather observations using downlink aircraft observations. HKO

implemented an AMDAR programme in Hong Kong in 2000 to receive aircraft

weather data from Australian and U.S. aircraft operating at HKIA.

2.2 Recent developments

2.2.1 ADS

Currently, the airspace of Hong Kong is covered by surveillance radars. As such,

ADS is usually not applied for surveillance and the trial on weather reporting using ADS

datalink has been suspended. Similar situations are known in other airspace in the

Asia/Pacific Region. Hence, there is a need to identify another alternative for downlink of

meteorological data. At the suggestion of HKO, the use of other possible solutions (ADS-B

and Mode S) for automatic MET air-reporting in the Asia/Pacific Region are being studied by

ICAO.

2.2.2 AMDAR

In 2003, with the assistance of CAD and the Cathay Pacific Airways (CPA), a trial of

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AMDAR data collection from one B747 aircraft commenced. After evaluation of the data

quality, HKO started the operational dissemination of the AMDAR weather reports via the

Global Telecommunications System (GTS), making the data to other weather centres

overseas. In particular, the data is also available at the two World Area Forecast Centres

(WAFCs) for the preparation of en-route weather forecasts for international air navigation.

Since September 2005, the Hong Kong AMDAR programme was expanded to provide

additional AMDAR reports from a total of six CPA aircraft. At present, HKO receives about

1,000 AMDAR weather reports daily directly from these aircraft.

In 2005, experiments were conducted in applying the AMDAR observations for

low-level windshear reporting. Windshear (i.e. headwind changes of 15 knots or more)

experienced by aircraft during the take-off phase was computed from the high-resolution

AMDAR reports (at 4-second resolution) received and compared with the Flight Data

Recorder (FDR) wind data (at 1-second resolution) recorded on the aircraft (see example in

Figure 1). The AMDAR wind reports showed good agreement with the FDR data in respect

of the altitude and headwind (along the runway direction) (Figures 2 and 3). In particular,

AMDAR data at 4-second resolution was able to capture the significant headwind variations

associated with windshear events.

2005-03-19 15:55Z Departure (118_744_32401_CX880)Head Wind vs Time

0

5

10

15

20

25

15:55:10 15:55:19 15:55:27 15:55:36 15:55:45 15:55:53 15:56:02 15:56:10

Time (UTC)

Hea

d W

ind (

knots

)

0

1000

2000

3000

4000

5000

Altitude

(fee

ts)

AMDAR - Head Wind FDR - Head Wind AMDAR - Altitude FDR - Radio Altitude Figure 1. A comparison of the headwinds provided respectively by AMDAR and FDR for

the same flight.

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Altitude (feet)

y = 1.04x - 76.01R2 = 1.00

0

500

1000

1500

2000

2500

0 500 1000 1500 2000 2500

AMDAR

FDR

Headwind (knots)

y = 0.93x + 0.34R2 = 0.94

-20

-10

0

10

20

30

-20 -10 0 10 20 30

AMDAR

FDR

Figure 2. Scatter diagram of altitude Figure 3. Scatter diagram of headwind

After consulting the users and stakeholders of the windshear alerting service at HKIA, it

is planned that these automatic AMDAR observations will be used in operational windshear

reporting to alert aircraft operating at HKIA in early 2006 through the Automatic Terminal

Information Service (ATIS) (see schematic in Figure 4) or via the Air Traffic Control (ATC).

The necessary data quality control and automated windshear identification algorithms are

being developed by HKO for operational implementation. This is first step in the world in

applying high-resolution AMDAR weather observations measured onboard in low-level

windshear reporting.

Figure 4. The automatic AMDAR observations transmitted from aircraft will be used in operational windshear reporting to alert aircraft operating at HKIA via the Automatic Terminal Information Service (ATIS).

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3 Uplink of Meteorological Data

3.1 Background

Data uplink facilities provide a means of sending weather products, in the form of text

or graphical format, directly to the cockpit. Data uplinks reduce potential misinterpretation

due to poor quality of voice communication, thereby reducing ambiguity in the transmitted

information. The workload of air traffic controllers can also be reduced as a result. More

variety of weather products, particularly information on hazardous weather such as low-level

windshear alerts, can be made available to the pilots. Pilots can receive the weather

information at regular intervals, or upon request. The availability of weather information in

graphical format in the cockpit could also enhance the situational awareness of the flight crew.

Flight safety as well as aviation efficiency could be enhanced as the most updated weather

information can be made available to assist the pilots to take appropriate decisions to avoid

hazardous weather and to optimize their routes during the flight.

A number of datalink applications for uplinking meteorological information to aircraft

have been established in the recent years. They include the Digital - Automatic Terminal

Information Service (D-ATIS) and Digital VOLMET (D-VOLMET) service. Both services

were introduced by CAD in Hong Kong in 2001 in parallel with the conventional voice

broadcasts. The D-ATIS provides the latest runway weather conditions at HKIA, in

particular low-level windshear and turbulence warnings, together with the other aeronautical

information important for landing and take-off operations. The D-VOLMET provides

operational meteorological (OPMET) information, including airport observations, forecasts

and warning of hazardous en-route weather. In the past couple of years, the number of

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uplink requests for D-ATIS messages has increased by four-fold to more than 20,000 requests

per month (Song and Fong (2005)).

3.2 User Requirements of Weather Information Uplink

Building on the success of D-ATIS in uplinking weather information to the cockpit,

HKO conducted a survey in early 2004 to solicit user requirements from pilots for further

developments of weather information uplink. A total of 66 replies from pilots of 10 airlines

were received. Specifically, windshear and turbulence alerts are identified by pilots as the

most needed weather product for uplink. Other products include radar and satellite images,

runway weather information and forecasts at higher frequencies. Further details of the

survey results can be found in Cheng (2004).

Windshear and turbulence are by nature transient and sporadic and so the

windshear/turbulence alerts generated from automatic systems are highly perishable. It is

desirable that the latest windshear and turbulence alerts be made available to the pilots,

particularly during the approach phase of the flight. Understandably, it is not possible to

relay the windshear and turbulence information to the pilot on a minute-to-minute basis (or

when a significant change occurs) via ATIS/D-ATIS. It would however be possible to do so

via data uplink, preferably using a dedicated data link. In this connection, HKO, in

consultation with CAD, airlines and pilots made an effort to identify cost-effective means for

uplinking windshear/turbulence products to cockpit.

3.3 Recent Developments of Weather Information Uplink

3.3.1 Uplink of windshear information

The feasibility of using an available technology : standard ARINC 623 message type “Terminal

Weather Information for Pilots (TWIP)” has been explored. TWIP was developed in the US for

uplinking Terminal Doppler Weather Radar (TDWR) information (including microburst and

windshear alerts, and precipitation information) to aircraft equipped with standard ACARS VHF data

link facilities and avionics supporting ARINC 623. Trial operations of TWIP in the U.S. in the

mid-90s were successful and well- received by users. Sample TWIP messages from the trials

are given in Figure 5. From pilot surveys, it was found that the pilots rated the TWIP

service positively and considered that it could provide more timely and accurate situational

awareness of terminal weather hazards. In view of the favourable responses from users on

the TWIP trial operation, it was employed in full operation at each of the 47 TDWR sites in

the U.S. from 1998 onwards.

In Hong Kong, local airlines were approached in 2005 to explore the technical feasibility

of a trial uplink of the HKIA windshear and turbulence alerts via TWIP. It turned out that

the aircraft avionics would require software upgrades to receive TWIP messages and such

upgrades were considered not cost-effective for the purpose of conducting a trial.

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Figure 5. Sample “TWIP” messages in US:

(a) text messages (on-screen version) – upper left corner

(b) character graphics (printed version) – middle

cockpit

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Considering that TWIP has been successfully implemented in the U.S. for uplinking

TDWR information to the cockpit and the corresponding procedures are already in place for a

number of U.S. carriers, HKO sought the collaboration of the Northwest Airline (NWA) to

test the capability to uplink the alphanumeric microburst and windshear alerts generated from

the Hong Kong TDWR to NWA aircraft operating at HKIA (Fahey et al, 2006). To date,

testing of the generation of TWIP messages from the TDWR alerts (Figure 6), and

ground-ground transmissions of TWIP messages from HKO to NWA host computer via the

ARINC AviNet Mail service have been successfully conducted. It is planned that

operational trial uplink to NWA aircraft will commence during the peak windshear seasons in

spring and summer this year.

01234567890123456789 0 1 2 3 4 5 6 7 8 9

VHHH 0429 TDWR TERMINAL WS INFO *MICROBURST ALERTS TDWR ALERT 30KT LOST BEGAN 0430

Figure 6. Sample TWIP microburst alert generated from the Hong Kong TDWR

3.3.2 Uplink of graphical weather products

Apart from the uplinking of textual windshear alerts mentioned in Section 3.3.1 above, a

number of recent developments in weather information uplink are taking place around the

world. In particular, model templates for the graphical display of SIGMET information of

en-route hazardous weather (including volcanic ash, tropical cyclones and other hazardous

weather such as icing, turbulence and thunderstorms) have been developed for incorporation

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into the international standard of ICAO and WMO. In particular, the model template for

tropical cyclone SIGMET (Figure 7) was developed by HKO (Wai, 2005). Concurrently,

HKO has also been tasked by ICAO to develop model template for future uplink of graphical

windshear and turbulence products. Work is also being progressed in the development of

guidance material for the display of meteorological information in the cockpit.

3.3.3 Communication channel s for uplink

Since more weather products, especially those in graphical format, are planned to be

made available in the future, communication channels with wider bandwidth for uplink

would be required. Due to the limitation of the air-ground ACARS VHF communications

bandwidth (2.4 kbps), only simple text-based information such as D-ATIS, D-VOLMET and

TWIP could currently be uplinked. In view of this, ICAO accepted HKO’s proposal to

identify a datalink to support future uplinking of graphical weather information (Shun, 2005)

and to develop relevant international standards and guidance to facilitate implementation.

One possibility is the new VHF Digital Link (VDL) - Mode 2 which has a larger bandwidth

(31.5 kbps) and is being progressively implemented in parts of North America, Europe and

Asia. Another possibility is the commercially available Internet service which has already

been launched by a number of airlines for use by in-flight passengers.

Figure 7. Graphical tropical cyclone SIGMET model template formulated by HKO.

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4 Conclusion

The new uplink and downlink technologies offer unprecedented opportunities for

meteorological services to transmit real-time weather information to and from

aircraft- in-flight for enhancing aviation weather services and ultimately safety, efficiency and

regularity of aviation. Their applications and values in windshear alerting at HKIA are

demonstrated. HKO will continue its efforts in developing other weather information uplink

applications to suit the needs of airlines and pilots, taking into consideration the latest

available technologies and international standards.

5 References

Cheng, C.M., 2004 : ‘Survey on Pilot's Requirement on Uplinking of Meteorological

Information’. ICAO Eighth Meeting of the Communications/Navigation/Surveillance and Meteorology Sub-Group (CNS/MET SG/8) of APANPIRG, Bangkok, Thailand, 12 - 16 July 2004.

Fahey, Thomas H., III, C.M. Shun, Amy VanGerpen, Junichiro Asano and Tuan Nguyen, 2006 : ‘Low Altitude Wind Shear Hazards : Ground Based Detection and Commercial Aviation User Needs’. 12th Conference on Aviation, Range, & Aerospace Meteorology, American Meteorological Society, Atlanta, GA, USA, 29 January - 2 February 2006.

Shun, C.M., 2005 : ‘Identification of a data link for uplinking graphical meteorological information’. ICAO Ninth Meeting of the Communications/Navigation/Surveillance and Meteorology Sub-Group (CNS/MET SG/9) of APANPIRG, Bangkok, Thailand, 11-15 July 2005

Shun, C.M., C.M. Cheng and H.G. Wai, 2003 : ‘Recent Developments to Enhance Windshear and Turbulence Alerting at the Hong Kong International Airport’. Proceedings of the 4th International Symposium on Electronics in the Air Transport Industry, SEATI 2003, The Institute of Electrical Engineers Hong Kong, p.46-60.

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Song, M.K. and Benjamin Fong, 2005 : ‘Current Status of D-ATIS and D-VOLMET

Implementation’. ICAO Ninth Meeting of the Communications/Navigation/Surveillance and Meteorology Sub-Group (CNS/MET SG/9) of APANPIRG, Bangkok, Thailand, 11-15 July 2005

Wai, H.G., 2005 : ‘Specification of Graphical Tropical Cyclone SIGMET for Uplink to

Aircraft’. ICAO Eighth Meeting of the Meteorological Information Data Link Study Group (METLINKSG/8), Montreal, 1 to 4 February 2005.